Accessibility: Keyboard focus

[cjcenizal]

Problem

By default, modern browsers provide keyboard focus indicators on interactive elements with native support for keyboard interactions. These indicators are highly visible, and inform users of focus location in a standard, predictable way (see components that are highlighted on focus). There are interactive elements with custom styling that are not visually distinct, and may not be visible to users with some visual disabilities (see the "Graph" page for an example). We should consider restoring the default keyboard focus indicators in addition to any custom styling, or follow the WCAG 2.0 recommendations for creating highly visible focus indicators.

Note: this can largely be addressed by compenentization via #9708.

Elements that require focus states

• Links
• Form elements
• Buttons
• Expand/collapse toggles
• Menus
• Tabs
• Side navigation
• Local navigation

Audit

We just need to go throughout Kibana and X-Pack and check the elements used in each user interface.

[timroes]

This should be done by now. If there are any places left this isn't done we should open a separate issue for that specific place, UI component, etc.